Method for photo-mechanical composition of designs on stencils for film and screen printing, particularly rotary screen printing

ABSTRACT

To improve the detail on screen printing, in which images are applied to a printing grid or screen in which a photo-sensitive layer is utilized to be exposed in accordance with the image or composition to be printed, and the non-exposed image portions are removed before printing, the screen is pre-processed to provide it with a smooth surface so that the photo-sensitive layer can, itself, be applied on the screen with a smooth surface of uniform and controllable thickness directly over the printing grid; in a preferred form, the interstices of the printing grid or screen are filled with a filler, and the surface of the grid and the filler is then treated to remove that portion of the filler which is above the grid elements, leaving the filler within the interstices, and a smooth surface over which the photo-sensitive layer can be applied. A plurality of such applications can be made, the photo-sensitive surface itself being exposed to form a lattice screen, which is treated to provide a smooth surface on which a further photo-sensitive layer which is to be exposed with the image, can then be applied.

lllite ttes Pate 1 lltlemrn 51 Sept. 17, 1974 [75] Inventor: MartinlKlemm,Gerlafingen,

Switzerland [73] Assignee: Fritz Buser AG., Maschinenfabrik,

Wilex near Utzenstorf, Switzerland 22 Filed: Apr. 6, 1972 21 Appl. No:241,609

[30] Foreign Application Priority Data Apr. 13, 1971 Switzerland 5265/71June 21, 1971 Switzerland 9055/71 Aug. 3, 1971 Switzerland 11432/71 [52]US. Cl 96/364, 204/11, 101/1282, 101/128.3,101/128.4 [51] Int. Cl G03c5/00 [58] Field of Search 96/36.4; 10l/128.2128.4; 204/11 [56]References Cited UNITED STATES PATENTS 734,120 7/1903 Deeks 101/12822,110,319 3/1938 Bell 2,282,203 5/1942 Norris 204/11 2,332,592 10/1943Norris 204/11 2,340,485 2/1944 Norris r 204/11 2,421,607 6/1947 Fowlerl0l/128.4

Primary ExaminerDavid Klein Attorney, Agent, or Firm-Flynn & Frishauf[57] ABSTRACT To improve the detail on screen printing, in which imagesare applied to a printing grid or screen in which a photo-sensitivelayer is utilized to be exposed in accordance with the image orcomposition to be printed, and the non-exposed image portions areremoved before printing, the screen is pre-processed to provide it witha smooth surface so that the photo-sensitive layer can, itself, beapplied on the screen with a smooth surface of uniform and controllablethickness directly over the printing grid; in a preferred form, theinterstices of the printing grid or screen are filled with a filler, andthe surface of the grid and the filler is then treated to remove thatportion of the filler which is above the grid elements, leaving thetiller within the interstices, and a smooth surface over which thephoto-sensitive layer can be applied. A plurality of such applicationscan be made, the photo-sensitive surface itself being exposed to form alattice screen, which is treated to provide a smooth surface on which afurther photo-sensitive layer which is to be exposed with the image, canthen be applied.

7 Claims, 14 Drawing Figures PATENTEDSEPITIHM 3.836.367

SHEET 1 0F 5 FIG.2

PAIENIEBsEPI 71914 I SHEU 2 OF 5 FIGA FIGS

FIG. 6b

The present invention relates to a method of photomechanically composingthe pattern to be applied on screens or grids for film and screenprinting, and more particularly for rotary screen printing, in which alightsensitive layer is removed in accordance with an image which isexposed on the photo-sensitive layer.

The term composition of an image on the screen, for purposes of thepresent application, is to be so interpreted that the screen will have apattern thereon which consists of open or closed interstices or spacesbetween the meshes of the screen, in accordance with the image to bereproduced. Screens or grids of this type may be used to print onvarious materials, such as textiles, paper or the like.

Rotary film printing is a special process of the more generally knownfilm or screen printing, in which screens or sieves in form of a hollowcylindrical stencil are used. The method of composition utilized isprincipally a galvanic composition process in which the sievelikeportions of a hollow, cylindrical round stencil are first galvanicallybuilt up in one operation, and then coated in which the galvanicallyproduced sieve, grid, or screen is covered with a photosensitive plasticlayer, or paint coating which is removed, in the course of the furtherprocess steps, at areas determined by the image to be reproduced. Inthose portions which are not to be printed, the coating remains; in theportions which are to be printed, the layer or coating of thephoto-sensitive material is removed. For a general discussion of thisprocess, reference is made to The Way Things Work, Simon and Schuster,1967.

The present invention relates to the screen or grid printing method inwhich a photo-sensitive coating is removed from the screen whereprinting is to be carried out, and is left on the screen where no printis to be made. In spite of the high state of the art in this field, themethod has some disadvantages, one of them being that the sharpness ofreproduction is not as high as might be desired see also comment in theabove referred-to literature reference. It has been found that the lackof sharpness or accuracy in reproduction is due to a step, orsawtooth-like edge at the ends or ter' minal limits of the figures; thishas led to the concept of sawtooth edgeformation, or distortion inconnection with lack of sharpness of reproduction in this process. To acertain extent, this undesirable effect can be reduced by printingmanipulation and handling; however, some distortion and lack ofsharpness has been accepted in this field as a disadvantage which cannotbe avoided.

It is an object of the present invention to provide a method ofphoto-mechanical composing of matrices for use in rotary printing inwhich the lack of sharpness, and particularly the so-called sawtoothdistortion at the edges of portions to be printed is eliminated or atleast reduced to be completely, unnoticeable.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly, the photo-sensitivelayer is applied to the underlying screen or grid as a surface havingconstant and controllable thickness of its layer when applied to thegrid stencil. In accordance with an embodiment of the invention, theinterstices between the grid are first filled with a material which canbe later on removed, the filler and the surface of the grid then beingprepared to have a uniform top surface so that the photosensitive layerto be applied thereover likewise will have a smooth surface ofcontrolled and uniform thickness.

The invention will be described by way of example with reference to theaccompanying drawings, wherein:

FIGS. 1 to 5 and FIG. 7 illustrate various steps in the composition ofthe image to be screen-printed;

FIG. 6a illustrates an intermediate step or result in accordance withthe prior art; and

FIG. 6b the same step in accordance with the present invention;

FIG. 8 is a schematic representation of a method used to reproduce afine line;

FIG. 9 is a cross section along line IX-IX of FIG. 8;

FIG. 10 is a perspective view of a grid stencil with a stencil layerhaving a fine raster;

FIG. 11 is a cross-sectional view, in highly schematic form, through astencil having a fine raster;

FIG. 12 is a schematic top view ofa stencil with a pattern or composinglayer, partly broken away, and in which rasters on stencil layers ofdifferent fineness have been applied; and

FIG. 13 is a perspective view of a stencil with two photo-sensitivelayers, in which the second layer is the composed layer.

The formation of unsharp edges, that is, the sawtooth formation isbelieved to be due to the interaction oftwo causes.

After drying, or polymerization of the emulsion layer, it has been notedthat the layer has a clearly defined top wavy layer, or undulatingsurface, entirely independent of the type of photographic emulsion whichis being used. This waviness or undulation appears to be due to theusually used rubber doctor blades during application of thephoto-sensitive emulsion. In connection with this technology, moreemulsion is applied in the interstices between the grids of the screenthan on top of the grid elements themselves. The still soft anddeformable emulsion may be smooth; upon the subsequent followingphysical drying step, however, the surface will become wavy since thoseareas which have a greater volume of emulsion, that is, between theinterstices, will shrink more than the ones which are thin.

These zones, after drying no longer flat, are then exposed through anegative, or through a slide. The light penetrates under various anglesinto the emulsion layer and, within the layer, is diffused in variousdirections. It is thus basically impossible to provide an edge of theimage which is three-dimensionally congruent with the negative, orprojected image from a slide, within the emulsion layer. This rathertheoretical fact beomes material in actual practice since exactly in theinterstice or opening of the rasters at which, for reasons of printingtechnology the highest accuracy in imaging is required, the greatestvolume of underlying layer is present, resulting as above noted, in thegreatest inaccuracy of imaging. Thus, if a raster opening is notpenetrated by light, that is, is imaged from a light impervious oropaque portion of the negative, that is, if a bridge across theinterstice would be formed, a complete closure of this opening willresult. Thus, the edge of the image does not follow the theoretical orideal line of the negative but the various intersticial openings of therotary matrix and thus the raster formation at the edge of the image.

Even if it would be possible to use collimated or parallel light forimaging, the desired ideal projection would not be achieved.Concomitantly, the bridging of the raster openings by the emulsion wouldresult. The sawtooth effect in printing would, however, still be visible(as can be seen, for example, in rotary matrices of low mesh number).The waviness of the emulsion layer does not permit best optimal contactat the cross-over points of the raster openings between the emulsionlayer and the substrate. This leads to an excess amount of printing ink,and flooding at the edge of the figure in the region ofjust these rasteropenings, so that the raster opening prints as if it would be completelyopen.

The sawtooth effect is due to two causes. The waviness of the emulsiondoes not permit accurate and adequate imaging of the negative, or slideto be projected, even if customary technology permits some bridging ofthe interstices; the waviness does not permit a tight sealing betweenthe emulsion surface and the substrate. Further, the interaction of thenon-uniform emulsion layers and the inclined, or non-parallel projectionwith non-collimated light as is customary, does not permit a sharpcongruent imaging of the negative during exposure.

Within the region of the screen printing with flat matrices, thereferred to sawtooth effect can be avoided by forming a so-calledprinting shoulder. In accordance therewith, the edge of the image whichis not to be printed is formed slightly raised. The angle at the edgeofthe image should be as close to a right angle as possible, and shouldbe sharp, so that rounded corners are avoided, if at all possible. Theraised, non-printing portion of the matrix should be capable of closelycontacting the material to be printed, such as a paper sheet, or textilematerial. This, then, results in optimum sealing between the portion onwhich printing is to be carried out, and the non-printing portion withrespect to the printing ink which, as above referred to, is not usuallypossible in the customary composing system for rotary stencils. Whenprinting flat, various methods which are well known have been proposedthe pure indirect methods, such as cut film, (pigmented paper methods)and the like; pure direct methods such as additional layering,Supernylonsol process (trademark) and the like, and mixed systems inwhich the pure direct method and the pure indirect method are mixed,that is so-called combined processes. All these methods and processescan be used with a printing edge, or printing projection and permitprinting without the sawtooth distortion. The disadvantage, however,resides that layers are produced which have low adhesion to the grid ormesh, or screen and have low chemical and mechanical stability as isnecessary for rotary screen printing and permit only shallow screens tobe applied to the printing cylinders. The specific loading ofthe stencilin rotary printing is substantially higher than in flat printing so thatuse of the above referred to processes is not possible even if thecylinders, and the stencils are not of large size. In order to composeimages on rotary stencils, emulsions have been developed which meet therequirements with respect to loading which, however, since used indirect processes which do not permit additional layering, result in theaforementioned sawtooth formation.

It is thus an object ofthe invention to avoid the disadvantages of theprior art, while being able to use the characteristic advantages of themethods referred to which are known within the technology of the flatscreen printing, that is, which utilize a precise printing shoulder orraised section, and still utilize a direct system in which a highstrength emulsion can be utilized.

Referring now to the drawings and particularly to the series of FIGS. 1to 7, in which the process is described, and contrasted with that of theprior art.

A screen surface, such as a cylindrical stencil is coated with a layer32 which can be dissolved in a known solvent, such as a filler lacquer(FIG. 1). The screen itself is shown schematically in cross section, andhas grid or mesh lines 1 separated by raster or grid interstices 2therebetween.

The surface of the screen, coated with the lacquer 32 is then buffed orground so that the grid surfaces, at their top, are freed from thelacquer 32, the interstices, however, remaining filled to form acomposite, level, smooth continuous surface FIG. 2. FIG. 3 illustratesthe next step, in which a photo-sensitive layer 33 is applied over theground and smooth surface formed of the combination of grid or meshelements I and the filled interstices 32. Layer 33 is dried, ascustomary. As schematically indicated in FIG. 4, a negative 5 is thenexposed by light beams 8. Negative 5 has transparent regions 7 andopaque regions 6.

After exposure, the layer 33 is developed see FIG. 5 and the exposednon-soluble regions 9 will remain on the surface of the screen.Comparing FIGS. 4 and 5, it will be seen that the light beams 8 whichpenetrate under various angles cannot have deforming effects at the edgeof the transition region between a grid and a grid interstice, since thelayer 33 is of uniform thickness, and, further, the thickness oflayer 33can be held at a predetermined desired thickness with respect to thewidth of the raster interstice 2. Thus, the previously referred tothree-dimensional imaging or composing process is controlled. Theformation of the so-called printing shoulder can also be effected,permitting optimal sealing between printing and non-printing regions orzones.

The remaining, photo-sensitive and exposed layer 9 is dried andpolymerized. This layer will shrink. Referring to FIG. 6a, which showsthis step in accordance with the prior art in which the interstices 2 donot have a filler 32, it will be seen that the shrunk region 9 has ashrinking zone 35. Comparing FIG. 6a with FIG. 6b, where the method inaccordance with the present invention is illustrated, it will be seenthat the photosensitive layer in known composing method shrinksthreedimensionally, and, further, that the deformation process due tothe shrinking of the emulsion layer is enhanced. In contrast, theemulsion layer 9' (FIG. 6b present invention) can shrink essentiallyonly in a twodimensional direction, that is, sideways of the top surfacelayer formed by the grid 1 and the filler 32, as illustrated at 35,since that portion of the emulsion 9 which overlies an intersticialarea, as seen at 4', will be supported from below by the layer 32. Thus,vertical (with respect to FIG. 6a or 6b) shrinkage of the exposedportion, as illustrated in FIG. 6a is not possible in accordance withthe present invention.

After polymerizing, an additional step is carried out in accordance withthe present invention, namely removal of the filler material 32 see FIG.7. The polymerized layer 9' is chemically highly stable and it has beenfound from experience that the usual solvents to remove the layer 32 donot affect layer 32. The printing shoulder 9" is flush with the topsurface of the layer 9'.

The process in accordance with the present invention provides for edgesof the figures which are free of sawtooth formation. Not only is itpossible to provide sharper reproduction, but fine detail, with finelines can be reproduced which was not heretofore possible.

The process in accordance with the present invention can also be used toreproduce half tones. The image to be composed is photographicallybroken into a line raster, for example, by a grid, a dot pattern or thelike, which is utilized in the form of a screen, or the like uponexposure of the image.

In usually known composing methods for rotary stencils, the width of thesmallest line which can be composed and readily printed, by experience,extends between two interstices and one grid line. It can readily beseen that the width of the line depends on the fineness of the mesh ofthe screen of the stencil. In other words, coarse rasters, if used,permit only wide lines, and fine rasters permit thin lines. Inaccordance with the present invention, the width of the line need onlyhave the width of one of the grid lines themselves, measured at theouter edge of the stencil.

In order to be able to compose even smaller lines and to print thesesmaller lines, which are essentially independent of the fineness of theraster and the stencil, the method can be modified, as explainedparticularly in connection with FIGS. 8 and 9.

Let is be assumed that the grid has been filled with a filler sustance,and then ground to form a smooth surface, to which a photo-sensitivelayer was applied which is thereafter exposed, in other words, that thesteps in connection with FIGS. I to 5 have been done. The line which isformed after washing and drying is indicated in FIG. at 40 which, as isclearly apparent, is less wide than the width of a screen element ii. Inthose cases in which the line falls congruent with a raster grid, adirect connection between a raster intersticial space is not provided,which provides for poor inking, and poor printing such a point.

In accordance with a feature of the invention, a communication can beprovided with the stencil after the polymerizing step of thephoto-sensitive layer has been carried out, but before the material 32,filling the intersticial spaces, has been removed or dissolved. Beforesuch dissolving, the exposed stencil is etched, but only from the sideof the grid at which the polymerized emulsion is placed. An etch bath isselected which has high lateral etching effects, but low depth etching.The filler substance which, during the etching step, is located only inthe intersticial spaces between the grid lines permits application ofthe etch material only to those points where it is needed, that is,where it can etch away some of the grid lines, where required, whichcontributes to the stability of the entire stencil. The etching processis terminated when openings 41 (FIG. 9) are formed by removal of somematerial from the grid II, that is, beneath or between the imaged line40 and the respective adjacent raster opening 2 which, at

that stage of the process, is still filled with the material 32.

After termination of etching, the filler substance 32 is dissolved orwashed out, and the stencil is ready for printing.

The usual grid material for rotary screens utilizes nickel almostexclusively and thus iron chloride, in an aqueous solution is a goodetch substance.

If the mesh openings are wide, that is, if the raster is quite coarse,such as 40 or 60 mesh, or if thick emulsions are to be used in theprinting, then high requirements are placed on the strength andsturdiness of the emulsion layer, due to the large bridges of emulsionover the raster openings. To obtain error-free printing also in such acase, and in spite of the high mechanical loading, the inner side of thestencil, ready for printing, may have a lacquer applied thereto which,immediately after application and while still somewhat flowable, isremoved from the emulsion side of the stencil by suction. After asuitable drying, that is, after chemical hardening, the emulsion layeris reinforced on the side which does not print, without interfering withthe quality of the print-ready stencil.

In accordance with a feature of the invention, finest image details canbe reproduced, independent of the fineness of the grid material itself.

Referring to FIG. 10, a grid or screen material 51 of any predeterminedfine, or coarse mesh size is used and, as above described, is filledwith filler material so that the grid lines are blank, but: theinterstices are completely filled, so that the grid with filler materialforms a smooth continuous surface. In a second process step, a suitablepattern carrier is used, for example one of the known photo emulsionswhich can be hardened, to copy a line raster on the smooth surface. Thisraster is developed and hardened. The pattern to be composed, and thento be printed is carried out in a third step, analogous to the second.The stencil surface which now has projecting grid lines has a suitablelacquer applied thereto, to fill the spaces between the grid lines. Thislacquer is then removed, for example by grinding or buffing until theraster lines 58 of the pattern are free at their upper surfaces 59 ofany filler lacquer; the interstices 60, however, between the patternlines 58 are filled and, together with the filling, form a smoothsurface.

The printing stencil which is so prepared then has the hardened photoemulsion applied thereover, which is exposed, in accordance with thesteps explained in connection with FIG. 4, and the hardened photoemulsion is then developed, dried and hardened. The last stencil layer62 (FIG. 10) then defines therebetween the open spaces 61 of the printstencil, where printing is to take place. In a last step, the fillerlacquer is washed out by a suitable solvent.

The dimensioning of the line raster 58, that is, the auxiliary pattern,as well as the distance of the lines from eachother depend on thephotographic resolving power of the stencil material which is to beused. Within the limits given by the stencil material, thin and highraster lines define a large quantity of ink available for printing; flatand wide raster lines provide only little printing ink. In order tochange the: relationship of ink available for printing, that is, tomatch the printing form to the substrate on which the printing is to becar ried out, the thickness ofthe stencil layer, that is, of the firstgrid pattern, can be changed by changing the thickness of the layer ofwhich the grid pattern is made, and the pattern itself can be suitablyvaried, by selectively using different photographic patterns.

The line raster, which is photographically applied, can thus be changedto control the volume of printing ink, and thus to vary the base stencilon which the image is composed. This line raster may have a furtherfunction. It may be desired, for example, to reproduce details which aresmaller than the free width of the interstices of the screen. Inaccordance with the usual methods, these details, when exposed on thescreen and if they are on a screen opening, could not initially have anyconnection with the underlying screen material, thus, could not besecured thereto. As illustrated in FIG. 11, details 52, if they were tobe reproduced, are not secured to the underlying grid material,schematically indicated at 1, and corresponding to the grid 51 of FIG.10. These elements 52 would thus fall through the interstices betweenthe grids. In irregularly arranged details, the reproduction of thecomposed image would thus be different from the image actually exposed.In regularly recurring patterns, for example in cross rasters, a moireeffect would invariably result.

In accordance with the described embodiment, these effects can beavoided. It is only necessary to make the line raster of the first,lower pattern on the stencil so fine that even the finest details of theimage to be composed will find support on the underlying grid pattern.

FIG. 12 illustrates the combination of a photographically resolvedimage, broken up into a 60-line raster which can be combined with a32-line raster (80 mesh) screen, without being subjected to a moireeffect.

The filled screen material SI first has a first line raster 58, forexample at 40 lines per centimeter applied thereto. Thereafter, and inaccordance with the previously described process steps, a second lineraster 63 of, for example, 60 lines ,per centimeter and arranged at anangle of, for example, approximately 90 with the first line raster, isapplied. A third layer 64 of the stencil material is then applied; theimage is composed over the raster of the last stencil material layer, inthis instance, in a 60-mesh cross raster. Of course, the structure ofthe last preceding line raster 63 previously was levelled, so that thenext layer could be applied thereto; the structure of the first lineraster 58 also previously had been ground or flattened or levelled. Thecross raster, with horizontal grid lines 67 and vertical row lines 68 isso arranged on the last preceding line raster therebeneath that the inkimpervious, horizontal line rasters 67 of the cross raster always fallon the lines of the second line raster 63 which are immediatelytherebeneath. The vertical row lines 68 of the cross raster are freelyself-supporting.

Some raster opening 69 may fall in the region of a raster line 58 of thefirst stencil layer 58. This is immaterial. The ink which is suppliedduring printing fills the line raster system which, in this embodiment,has three layers of material. In view of the raster grid lines 58, 63,it can enter the raster opening 69 of the last stencil layer 64 due tothe interstices, even those which are apparently covered. As a result, ascreen printing system is developed which, in the light of the state ofthe art, provides an extremely fine break-up of the image to bereproduced, by providing a very fine cross raster therefor.

The actual layer which is formed in accordance with the image is notapplied to the basic grid raster, but rather on layers of material whichthemselves are formed in a raster stencil, before the final layer onwhich the composition is imaged, has been applied. Thus, the amount ofink which is needed can be accurately controlled by controlling theso-called ink volume of the raster, or underlying screen in accordancewith design requirements, that is, by forming the underlying rasters atspacings and in arrangements to match the ink which is needed. Further,by the combination of various rasters, the detail of the image to bereproduced becomes essentially independent of at least the bottom-mostof the underlying grid layers, and the detail of the image to bereproduced can thus approach the limits of the photographic resolvingcapacity of the stencil material. The detail is thus independent of thematerial and grid raster size of the basic grid and screen or gridprinting of color tones or scale which are resolved into a broken-upimage can be obtained, without a moire effect.

In accordance with the process described in connection with FIGS. 10 to12, the first light-sensitive layer is exposed and then processed, bydeveloping, hardening, and the like before the second light-sensitivelayer is applied thereover. This process can be simplified in that thefirst light-sensitive layer is not completed, that is, is not developedand hardened and, likewise, preparation of the first light-sensitivelayer by filling with filler material and subsequent flat grinding andpolishing is not done before application of a second photosensitivelayer. Rather, after exposure of the first lightsensitive layer, asecond stencil material layer is applied thereover. This substantiallyreduces rejects and errors, as well as work time and material and thusresults in lower costs. The printing shoulder is formed in somewhatsimpler manner than in the process in accordance with FIGS. 10 to 12,and the ink penetration of the screen grid material can be limited. Thismodification of the process is illustrated in connection with FIG. 13.

A base screen having grids 71, with openings 72 therebetween is the basematerial, filled with a filler in such a manner that, on the one hand,the grid raster lines are not covered and, on the other, the gridopenings are completely filled. In other words, the initial filler isapplied to the base grid which is then ground or polished to a smoothsurface.

In a second stage of the process, the smooth flat grid material, withthe interstices filled, has a photosensitive stencil layer appliedthereto, which is then dried. This stencil layer is exposed through amask which may only show lines, that is, through a line-ruled mask,negative, or slide. In a third step of the process, the now exposedstencil material layer has a second photo-sensitive stencil materiallayer 75 applied thereto. Since the underlying surface is flat andsmooth, the second stencil material layer 75 will likewise be flat andsmooth.

The second stencil material layer 75 is then exposed through an imagenegative, which carries the composition to be applied to the screengrid. In a fourth stage, the second layer 75 is exposed which, again,also exposes those portions of the first photo-sensitive layer whichreceive light through the slide or negative carrying the composition,and which were not exposed during the first exposure. The alreadyexposed portions,

however, which are again exposed by the second exposure receive twicethe light; this is no disadvantage when the known and easily polymerizedphoto emulsions are used.

ln a last step of the process, the entire stencil material is developed,hardened, and thereafter the filler material in the interstices 72 isremoved, so that the final printing screen or grid is finished.

The line raster 73 permits reduction of the ink penetration in the gridmaterial, as desired. The dimension of the remaining lines '73 (FIG. 13)can be changed, and the thickness of the layer of these line rasters,indicated at 76, can likewise be changed, to provide a controllablereservoir for ink. The width of the lines of the line raster, and theirorientation of course is determined by the mask which is used for itsexposure; the thickness by the thickness of the photo-sensitive layer.The second photo-sensitive layer 75 has a thickness indicated at 77(FIG. 13) which again can be varied as desired. It is applied on theexposed first layer, the two photo-sensitive layers having a combinedthickness indicated at 78. The difference in height 77 of the secondlight-sensitive layer 75 with respect to the thickness 76 of the firstlayer 73 provides for the desired shoulder 50 at the edges of the image.

Exposure of the second layer 75 over the image carrying negative exposesall regions 79 of the first photosensitive layer 73, which were notprovided to permit ink to penetrate in the first place. By thisexposure, the stable and sturdy interconnection of the two layers, asindicated at 74, will result, both with respect to each other as well aswith respect to the underlying grid material. Good stability is obtainedalso on the bridge points of the raster opening 72.

The substance which has been referred to as filler, or filler lacquer,to be used in the present invention must have these characteristics:ease of application by usual application techniques; non-foaming;hardening and capability to be ground or polished by utilization ofusual and customarily available grinding and polishing techniques;non-solubility in water; freedom from shrinking, also over longerperiods of time (twelve months or longer); freedom from shrinking overshort periods of time upon heating, for example in the region of 200 C,and for periods of from 3-4 hours; good adhesion to the usual grid orscreen materials utilized in rotary screen printing technology,particularly nickel, and independent of aging and temperature up to 200C; low thermoplastic flow, even if heated to temperatures to 200 C; goodsolubility before and after heat treatment in solvents which do notattack the polymerized layer; chemical resistance with respect tousually used etching solutions, such as ferrous chloride, and,additionally, non-poisonous in use. Such a substance having the requiredcharacteristics are known as Plusodur 230, 60 percent Xylol, hardenedwith Maprenal RT, in a mixture of about nine parts Plusodur 230 and onepart Maprenal RT (by weight). As solvents, ketones and esters can beused.

The invention has been described particularly in connection with rotarystencils for rotary presses, but can be used equally for flatbed pressesand flatbed stencils.

Various changes and modifications may be made within the scope of theinventive concept.

I claim:

til

ll. Method to make stencils having a stencil layer on printing gridshaving interstices between the grid lattice thereof, in which aphoto-sensitive layer is utlized to be exposed in accordance with animage to be composed 5 or printed, the non-exposed imageportions beingre moved before printing, the method comprising forming a level, smoothcontinuous composite sur face of exposed grid lattice and a solublefiller located only in the interstices between the grid lattice, byfilling only the interstices between the lattice grid with the filler;applying a continuous single photo-sensitive layer of sufficientthickness to form the stencil directly over the smooth surface of theexposed grid lattice and the filler in the interstices between thelattice with constant, controllable thickness; imaging an image in theform of a support pattern non-congruent with said grid lattice on thephotosensitive layer;

developing the support pattern image;

filling the spaces formed between the support pattern with a filler, thesurface ofthe filler and the support surface being level and smooth;

applying a further light-sensitive layer as a smooth surface withuniform controllable thickness over the smooth pattern and fillersurface;

exposing the further photo-sensitive layer with the image to becomposed;

selectively removing a portion of the layer of photosensitive materialin accordance with the image to which the layer was exposed to developthe ex posed photo-sensitive layer;

and thereafter removing all the filler material by a solvent.

2. Method according to claim 1, wherein the support pattern is a rasterand the first imaging step comprises imaging a raster on the firstlayer, developing and setting said raster to provide a base raster, saidbase raster 40 forming the screen grid for said further photo-sensitivelayer;

and filling the spaces between the developed and set raster with afiller material to provide said level and smooth surface.

3. Method according to claim 11, wherein the support pattern is a rasterand the first imaging step comprises imaging a first additional rasteron the first layer which has a raster different from the raster of thegrid;

the exposure step comprises exposing the further layer by imaging asecond additional raster on the further photo-sensitive layer, saidsecond and first rasters being different from each other; developing andsetting said first raster;

and applying a further light-sensitive layer, as a smooth surface, withuniform controllable thickness over the first and second light sensitivelayers, and after exposure, development, and setting thereof.

4. Method according to claim 1, wherein the step of filling theinterstices comprises applying a filler material over one side of theprinting grid, and penetrating 65 the interstices between the lattice ofthe grid; and

removing that portion of the filler material which extends over theprinting grid to leave a smooth surface of grid lattice and intersticialfiller material,

the photo-sensitive layer being applied over said smooth surface.

5. Method to make stencils having a stencil layer or printing gridshaving interstices between the grid lattice thereof, in which aphoto-sensitive layer is utilized to be exposed in accordance with animage to be composed or printed, the non-exposed image portions beingremoved before printing, the method comprising forming a level, smoothcontinuous composite surface of exposed grid lattice and a solublefiller located only in the interstices between the grid lattice, byfilling only the interstices between the lattice grid with the filler;

applying a continuous single first photo-sensitive layer of sufficientthickness to form the stencil directly over the smooth surface of theexposed grid lattice and the filler in the interstices between thelattice with constant, controllable thickness; exposing the firstphoto-sensitive layer with radiation in accordance with a first patternand, without further treatment of the first photosensitive layer,applying a further layer of photo-sensitive material over said firstphoto-sensitive layer with constant and controllable thickness; exposingthe further photo-sensitive layer with radiation in accordance with asecond pattern; selectively removing a portion of the layer ofphotosensitive material in accordance with the patterns to which thelayers were exposed to develop the exposed photo-sensitive layers;

and thereafter removing all the filler material by a solvent.

6. Method according to claim 5, wherein the radiation pattern of thefirst pattern is a raster;

and the further layer is utilized as the layer adapted to carry theimage to be printed.

7. Method according to claim 5, wherein the step of filling theinterstices comprises applying a filler material over one side of theprinting grid, and penetrating the interstices between the lattice ofthe grid; and

removing that portion of the filler material which extends over theprinting grid to leave a smooth surface of grid lattice and intersticialfiller material, the photo-sensitive layer being applied over saidsmooth surface.

2. Method according to claim 1, wherein the support pattern is a rasterand the first imaging step comprises imaging a raster on the firstlayer, developing and setting said raster to provide a base raster, saidbase raster forming the screen grid for said further photo-sensitivelayer; and filling the spaces between the developed and set raster witha filler material to provide said level and smooth surface.
 3. Methodaccording to claim 1, wherein the support pattern is a raster and thefirst imaging step comprises imaging a first additional raster on thefirst layer which has a raster different from the raster of the grid;the exposure step comprises exposing the further layer by imaging asecond additional raster on the further photo-sensitive layer, saidsecond and first rasters being different from each other; developing andsetting said first raster; and applying a further light-sensitive layer,as a smooth surface, with uniform controllable thickness over the firstand second light sensitive layers, and after exposure, development, andsetting thereof.
 4. Method according to claim 1, wherein the step offilling the interstices comprises applying a filler material over oneside of the prinTing grid, and penetrating the interstices between thelattice of the grid; and removing that portion of the filler materialwhich extends over the printing grid to leave a smooth surface of gridlattice and intersticial filler material, the photo-sensitive layerbeing applied over said smooth surface.
 5. Method to make stencilshaving a stencil layer or printing grids having interstices between thegrid lattice thereof, in which a photo-sensitive layer is utilized to beexposed in accordance with an image to be composed or printed, thenon-exposed image portions being removed before printing, the methodcomprising forming a level, smooth continuous composite surface ofexposed grid lattice and a soluble filler located only in theinterstices between the grid lattice, by filling only the intersticesbetween the lattice grid with the filler; applying a continuous singlefirst photo-sensitive layer of sufficient thickness to form the stencildirectly over the smooth surface of the exposed grid lattice and thefiller in the interstices between the lattice with constant,controllable thickness; exposing the first photo-sensitive layer withradiation in accordance with a first pattern and, without furthertreatment of the first photosensitive layer, applying a further layer ofphoto-sensitive material over said first photo-sensitive layer withconstant and controllable thickness; exposing the furtherphoto-sensitive layer with radiation in accordance with a secondpattern; selectively removing a portion of the layer of photo-sensitivematerial in accordance with the patterns to which the layers wereexposed to develop the exposed photo-sensitive layers; and thereafterremoving all the filler material by a solvent.
 6. Method according toclaim 5, wherein the radiation pattern of the first pattern is a raster;and the further layer is utilized as the layer adapted to carry theimage to be printed.
 7. Method according to claim 5, wherein the step offilling the interstices comprises applying a filler material over oneside of the printing grid, and penetrating the interstices between thelattice of the grid; and removing that portion of the filler materialwhich extends over the printing grid to leave a smooth surface of gridlattice and intersticial filler material, the photo-sensitive layerbeing applied over said smooth surface.